1. Field of the Invention
This invention relates to a method and structure for insulating separate power circuits of overhead electrical contact lines used by light rail vehicles and the like and more particularly relates to a structure which prevents arcing between such power circuits as the vehicle's current collector passes along such lines.
2. Description of the Prior Art
Electrified light rail vehicles, trolleys, small railroad trains and the like use a pantograph contact, shoe contact or other type of current collector to supply the vehicle with power from a suspended overhead power line. Such overhead lines generally utilize a plurality of separate circuits along their length separated by insulators. The problem of arcing between the circuits in the prior art occurs when the pantograph or other current collector passes from one circuit to another along the overhead power line. Such arcing between the circuits creates significant heat and causes damage to the power lines and to the section insulators between the separate circuits which damage shortens the useful life of the power lines. This arcing problem is especially significant when the traveling pantograph or shoe does not bridge the gap between the two power circuits as it passes across the section insulator. Under normal conditions arcing occurs on the contact wire as the pantograph passes on to the insulator, and pitting will cause a decrease in the cross-sectional area of the wire over time which worn areas must be replaced with pieces of new contact wire on a periodic basis because if not frequently replaced, the contact wire will fail and break.
Structures in the prior art have tried to minimize this arcing effect such as suggested in U.S. Pat. No. 4,320,820 to Elbert for a Section Insulator with Improved Arc Control which discloses a system of changing current paths to redirect magnetic fields to cause the arcs to move in a direction away from the section insulators. Others have approached the problem in a different way. S. H. Short's Multiple Arc Railway System patented in 1892 in U.S. Pat. No. 473,361 sectionalizes a long piece of contact wire fed from one generator into many short sections where each is isolated by a separate fuse which allows sections to remain energized while other sections can be repaired. Problems with this type of structure include service disruption and the necessity of frequent fusible element replacement. Others have approached the problem using diode arrangements and quenching circuits controlled by SCR loops such as U.S. Pat. No. 3,833,820 to Itoh issued Sept. 3, 1974 and West German Patent 2841434 to Siei. In Morq, USSR Patent 1303456 it is suggested to divide the overhead system into sections. Another USSR patent which Applicant believes is the most pertinent of the prior art to the instant invention is No. 1339040 to Lupo. The Lupo patent utilizes contact wire and supporting messenger wire overlaps at anchor locations. The anchor locations are composed of two separate catenaries (contact wire and supporting messenger wires) which are parallel with the messenger above the contact wire, and overlap a distance so that the pantograph travels along the contact wire of one catenary and then on both contact wires (the overlap) and then on to the other contact wire of the other catenary. The current collector does not travel on the messenger but only on the contact wire. A typical overlap can be from 3-30 meters in length depending on the type of line construction and voltage. Insulating links with neutral inserts are attached to the contact wire, and the pantograph passes from the first circuit's contact wire by the first insulating link, by the central insulating link, by the second insulating link, and then onto the second circuit contact wire. During this passage an arc is created when the pantograph passes from the first contact wire through the insulating links, and the created arc is deionized in time due to the passage of current through a diode chain. This structure is designed for use on alternating current electric railroads using a catenary support system and requires heavy overlapping-type construction where anchoring locations in such catenary system must have additional poles with support spans and bracket arms with significant extra hardware. The structure cannot be placed at other locations on the line unless a specific overlap anchoring system is first installed. This structure is also subjected to significant electrical wear from half-wave arcing since it diminishes, but does not eliminate, the arcing factor. There is always the possibility of a locomotive or vehicle stopping with its pantograph between contact wire and the insulating link which, if occurring, would cause a continuous electrical arc to be drawn due to the auxiliary loads of the vehicle (heat, light, and compressor) and such arc would continue to burn until the contact wire was broken.